David Brat, a little-known college professor from Virginia, shocked political observers nationwide this week when he upset one of the nation's most powerful Republican lawmakers by 10 percentage points with little outside support. Tennessee Tea Party activists hope a similar feat can be achieved here.

In the past few days, Brat's win has meant fresh invitations for Carr to appear on national talk shows, and the possibility that new funds and volunteers could be infused into a campaign that has trailed far behind Alexander's financially and organizationally.

But recent history suggests that the odds remain against Carr, political observers say. Other Tea Party challengers have received as much interest or more, only to fall short on election day. And unlike Cantor, Alexander has moved early to contain the threat of an upset.

"If I were Joe Carr, I'd certainly try to seize on (Cantor's defeat)," said John Geer, a professor of political science at Vanderbilt University. "I think his problem is the comparisons just don't fly."

Several polls, including at least one commissioned by a Tea Party group, have shown Carr trailing far behind Alexander. Only about one in five likely Republican voters supports Carr, while about half say they have never heard of him.

Carr has been on the campaign trail since last summer, but he has been hampered by a lack of national support. Federal Election Commission records show he has brought in about $866,000 and spent about $400,000. Alexander, by comparison, has raised more than $5 million and spent more than $3 million.

National Tea Party groups haven't provided Carr any help, but he does have the support of those within the state.

In recent weeks, the Carr campaign has tried to build on that base - and raise interest in his campaign - by rolling out endorsements from his fellow state lawmakers. Carr says 20 legislators back him. The strategy has generated little publicity.

But Cantor's defeat has meant an immediate jump in attention for Carr. He was interviewed on the day after the Virginia primary by CNBC and by Fox News host Sean Hannity. On Friday, he appeared on the radio show hosted by Laura Ingraham, one of the few national commentators to take an interest in Brat before his upset.

The attention has energized his supporters.

"Interest has just exploded," said Ben Cunningham, one of Tennessee's leading Tea Party activists. "We just have to redouble our efforts to get the message out."

Carr and his supporters say there is reason to believe Alexander can be defeated. They note that the past two Vanderbilt polls, conducted in December and May, have put Alexander's statewide approval rating at 49 percent - a level that indicates an incumbent is vulnerable.

Carr said his doubters have failed to account for voters' dissatisfaction with Congress.

"People are using conventional political wisdom that doesn't apply in unconventional political times," he said.

But those doubters say the comparisons between Cantor and Alexander are faulty. While Cantor focused on the speakership, Alexander gave up his leadership position more than two years ago. That has freed him to focus on his re-election effort and issues specific to Tennessee, such as regulation of compounding pharmacies and loosening restrictions on fishing near dams.

Alexander's supporters also note that Carr has to contend with other challengers in the primary. One of those contenders is George Flinn, a wealthy Memphis physician who has high name recognition in west Tennessee after having run for Congress four years ago.

"The parallel to the Tennessee race is South Carolina," said Whit Ayres, a pollster working with Alexander's campaign. "There were six challengers who ran in that race and (incumbent Sen. Lindsey Graham) defeated all of them by 41 percentage points."

Whether Carr can make the race close depends on him, said Geer, the Vanderbilt political scientist. And unless he starts to do so quickly, he is likely to suffer the fate of most Tea Party challengers - a burst of attention followed by defeat on election day.

"The Tea Party has not done well nationwide. Republican incumbents have usually won," he said. "There's still an enormous gap, and at the end of the day, it's going to depend on the quality of the candidate."